This application claims priority of U.S. Provisional Application Ser. No. 60/218,340, filed Jul. 14, 2000 entitled “Remote Laser Beam Delivery System and Method for Use with a Robotic Positioning System for Ultrasonic Testing Purposes,”, and is incorporated herein by reference in its entirety.
Additionally, this application is related to and incorporates by reference U.S. patent application Ser. No. 09/416,399 filed on Oct. 10, 1999 entitled “METHOD AND APPARATUS FOR DETECTING ULTRASONIC SURFACE DISPLACEMENTS USING POST-COLLECTION OPTICAL AMPLIFICATION” to Thomas E. Drake.
It is desirable for a variety of applications to provide for mechanically directing a laser beam to any location within a predetermined volume or on a surface. Many of these applications are tailored specifically for use within industrial manufacturing applications employing automated, robotics systems. Over the past several decades, the advent of robotics and laser light source technologies have led to many integrated systems for assembly line manufacturing. For example, robotics assembly systems incorporating laser technologies are very typical in automobile and even aircraft manufacturing plants for performing such tasks as welding.
For many systems, a robotic or gantry positioning system having a mechanical armature is often used to direct a laser beam to a variety of locations of a single workpiece. This armature itself provides for precision directing of the laser beam from the end of the mechanical armature. A laser beam delivery system is normally integrated into the gantry positioning system (GPS), particularly into the mechanical armature, for directing the laser beam from the end of the mechanical armature to any location within a predetermined volume. Specifically, the laser beam is then directed to portions of a workpiece and often from various fields of view for welding, cutting, ablating, or any variety of applications employing a laser beam.
Ultrasonic testing is a method which may be used to detect material defects in a objects comprised of various materials. A common application for ultrasonic testing is to detect inhomogeneities in composite materials. Ultrasonic testing may be used to serve a variety of industrial needs including identification of defects in manufactured goods for tuning of manufacturing processes. Manufacturers of products comprising composite material may wish to identify imperfections in their articles of manufacture to modify their manufacturing process to strive for greater repeatability and efficiency in their process or simply to identity problem areas within their process. Composite materials comprise many critical components within modern, high performance aircraft, and are becoming more common in terrestrial applications such as the automotive industry. Composite materials are desirable for many of their inherent attributes including lightweight, high strength, and stiffness. Particularly for aircraft application, those composite material components, which may be large and complex in shape, are often flight critical necessitating strict assurance of material and structural integrity.
Unfortunately, these materials are sometimes fabricated with imperfections or develop them after several hours of use. These material defects may appear as a delamination of the surface of the material, porosity, an inclusion, debonds between bonded sub-components, or a void within the component itself. This inhomogeneity in the structure severely weakens it, providing a situation which might result in catastrophic failure. A conventional method for detecting material defects in a composite material utilizes piezoelectric transducers in conjunction with mechanical scanners mounted across the surface of the composite to detect any material imperfections. The disadvantages of the conventional methods are many, including difficulty in accommodating non-flat or evenly mildly contoured composite materials. Another disadvantage is the requirement that the transducer couple to the material via a water path. The transducer must remain normal to the surface within ±3° during a scan. To accommodate highly contoured and complex shaped components using conventional techniques often requires extremely time-intensive test set up preparation.
Laser ultrasonic testing is an alternative method that is used to identify these imperfections. For aircraft applications, particularly for military fighter aircraft, all flight critical parts fabricated of composite material must be fully inspected before installation. A GPS comprising a laser beam delivery system may be integrated with a laser ultrasonic testing system for providing automated identification of material defects of a test object.
One approach is to mount the laser ultrasonic testing system comprising a laser source on the end of the mechanical armature of the GPS. The use of a GPS allows the ultrasonic testing system to be maneuvered around the test object to provide for positioning the laser source in close proximity to the test object from a multitude of locations of fields of vision. For those ultrasonic testing systems which use high power gas lasers such as CO2 lasers, the large and bulky size of the laser complicates the integration of the ultrasonic testing system with the GPS as the end segment of the mechanical armature must be capable of supporting a significantly heavy weight at its end. The large size and bulky weight of the light source itself often demands the use of a very large GPS capable of supporting the heavy weight of an ultrasonic testing system as it is maneuvered around the test object to perform data acquisition from a variety of perspectives.
Many typical laser testing systems are hampered when the ultrasonic energy generator is not positioned properly relative to the part to be tested. When this happens, the test results may need to be corrected, or in the case of testing relative strengths of different parts, this test may be completely inconclusive. Further, when the ultrasonic signal is generated, the resulting ultrasonic signal affects certain areas and/or volumes of the tested object. To completely test an object requires that a signal ultrasonic event be generated many times throughout various places on the surface and interior to the object. By doing this numerous times, the complete object may be tested, even though some areas affected may be common to others. In this case, many systems that rely on manual positioning err on a conservative side. This results in hugely overcompensated testing of the part since the overlaps are huge. Precise positioning of the ultrasonic testing device allows for scalable and efficient economies in the testing process, since the area of overlaps may be minimized.